We investigated the use of landmarks by capuchins to solve spatial search tasks. In Experiment 1 one subject learned to find a hidden reward in the middle of a 4-landmark configuration. During probe trials, with the landmark configuration expanded and no reward, the capuchin mainly searched near 2 of the 4 landmarks, thus showing it used the landmarks as beacons. In Experiment 2 two subjects learned to find a reward halfway between 2 landmarks, with the inter-landmark line variously oriented with respect to the room. During probe trials, with the landmark configuration expanded and no reward, the capuchins no longer searched in the middle of the landmark configuration. The capuchins searched between the landmarks, but at the training distance from each landmark separately. To do so, the capuchins may have memorized a certain distance to cover, beginning from a landmark, or exploited different types of perceptual information. Therefore, the capuchins use nearby landmarks to locate a goal, but not configurationally. We compare the results with those of previous studies with other animal species and discuss them in relation to issues of spatial cognition.

In this study we show that bonobos and capuchin monkeys can learn to search in the middle of a landmark configuration in a small-scale space. Five bonobos (Pan paniscus) and 2 capuchin monkeys (Cebus apella) were tested in a series of experiments with the expansion test paradigm. The primates were trained to search in the middle of a 4- or 2-landmark configuration, and were then tested with the same configuration expanded. Neither species searched in the middle of the expanded 4-landmark configuration. When presented with a 2-landmark configuration and a constant or variable inter-landmark training distance, the subjects sometimes searched preferentially in the middle of the expanded configuration. We discuss 2 alternative explanations of the results: extracting a middle rule or averaging between different goal-landmark vectors. In any case, compared to adult humans, primates appear highly constrained in their abilities to search in the middle of a configuration of detached landmarks. We discuss some of the factors that may influence the primates' behavior in this task.

We examined the ability of capuchin monkeys to use video without immediate visual-kinaesthetic feedback as a source of information to guide their action in the 3-dimensional world. In experiment 1, 2 capuchins learned to retrieve food under 1 of 2 different objects in 1 cage after watching the experimenter hiding food under 1 of 2 replica objects while in another cage. Information space and retrieval space were thus separate. The performance criterion was 71% first correct choices in blocks of 24 trials. However, when the subjects watched prerecorded videos of the hiding events, they chose randomly. In experiment 2, we gave the capuchins further trials with video and we enhanced the object shapes by line drawings. One capuchin eventually learned to use the video clips to locate food and he generalized this learning to 2 new objects.